I have started growing food on my farm, and I was wondering how long it takes to grow.

I planted my crops in the early hours of this morning, before the normal server/daily quest reset time but after midnight server time. I have heard two theories regarding how long your crops take to grow;

24 hours from the point in time they were planted, ie: if you plant at 2am, they will be ready the next day at 2am

At midnight, ie: if you plant at 11pm, at midnight your crops will be ready for farming

How does farming work in World of Warcraft? When will my crops be ready?

Crops now have a debuff which shows a timer of how long is left before their state changes from "Growing" to "Ripe" (or Plump). Since patch 5.1, this is synchronised with the daily quest reset timer. Therefore your crops will finish growing at the following times;

Your crops will become ready for harvesting at midnight server time - this means that regardless of the time of day you plant your crops (including 11:59 server time), your crops will be ready at midnight.

This is an outdated answer. With 5.1 the Crops now grow when your dailies reset on your server. For the most part, this will be 3am within the servers respective timezone.
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jakeisonlineMay 30 '13 at 10:10

As noted in your answer - this needs testing on the European realms (which is where I'm located) to confirm this change was applied to all servers. The source you've linked doesn't seem to indicate anything was changed on the European realms since the change was to counteract an American-specific exploit.
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kalinaMay 30 '13 at 10:12

After you plant your crop and do anything else necessary for it to survive. Click on the crop again and it will have a timer under it. Do the math with the server time or your own time depending on how you have it set. Then you will know when your crops will be ready every time.